The present invention relates to controlling vibration in surfaces and in particular relates to a system for controlling and/or damping vibration of dynamic surfaces.
In many industries, such as paper making, food processing, and textiles, or any other industry that processes a web of material, rolls are used for various processing functions, and in many instances, the stability of the roll is very important. For example, in a paper making assembly, roll vibration may cause variations in the thickness of the product being produced. Thus, it is desirable for the rolls to be as stable as possible and devoid of any imperfections, deflections or variations so that the paper being formed will be smooth and uniform. In addition to resulting in the production of inferior products, roll vibration may also result in damage to the roll itself or the machinery containing the roll. Thus, various attempts have been made to control vibration of rolls so as to avoid these problems.
One response to this problem has been to lower the rotational speed of the rolls in order to avoid or correct vibration-induced defects.
U.S. Pat. No. 5,961,899 to Rossetti et al. discloses a vibration control apparatus for processing a calendered medium that controls vibration between two or more rolls by controlling vibration induced thickness variations in a medium exiting from a nip. The apparatus includes a frame, first and second rolls relative to the frame and a force generator, such as an electromechanical active actuator, a servo-hydraulic actuator, a controllable semi-damper, and Active Vibration Absorber (AVA), or an Adaptive Tune Vibration Absorber (ATVA), providing canceling forces to control vibration between the first and second rolls, thereby controlling vibration induced thickness variations in the calendered medium. In certain preferred embodiments, the apparatus includes at least one sensor for providing a signal indicating a vibration condition of at least one of the first and second rolls, and a digital controller for controlling the signal representative of the vibration condition according to a feed-forward-control and providing a control signal to a force generator. Vertical and/or lateral vibration of the rolls may thus be controlled simultaneously. In addition, fundamental vibrational frequencies and their harmonics may be controlled individually, or in combination.
U.S. Pat. No. 5,447,001 to Nishimura et al. discloses a vibration control device for buildings. In one preferred embodiment, a building has mounted on its roof a hollow concrete-steel first mast carried on damping rubber supports. Within the hollow of the first mast, a second mast is mounted on anti-friction rollers, which roll on a low coefficient of friction interior floor of the first mast. The first and second masses are interconnected with a single element to vibrate these masses with a period of vibration that can be synchronized with the vibration period of the building to attenuate building vibration.
U.S. Pat. No. 5,403,447 to Jarvinen et al discloses a system in a press section of a paper machine for monitoring and controlling the running of a press felt. The press felts are guided by rolls having axial directions that are altered by means of an actuator so as to control the running of the press felts. The system includes detector devices for detecting one or more alignment stripes on the felts and oscillation detectors for detecting oscillation of the press rolls. The system also includes a microprocessor base controller for monitoring signals fed to the controller from the detectors. The controller analyzes the detector data in order to detect any felt-induced oscillations. The control system then generates signals for regulating the actuators of the guide roll that guide the running of the felts so that when the oscillation levels of the press rolls rise above certain limits, the direction of the guide roll on the felt that causes the oscillation is turned until an acceptable level of oscillation and/or a level of oscillation is reached.
U.S. Pat. No. 4,902,384 to Anstotz et al. discloses a wet press having vibration control. In one preferred embodiment, a wet press of a papermaking machine includes a pair of rolls defining a roll gap through which the paper being treated passes. The felt is guided in a closed loop path by additional rolls, which include a tightening roll. The tightening roll can be tilted to reduce roll vibrations by tightening the felt to set vibratory marks formed in the felt at an angle relative to the transverse width of the felt and the roll gap. A controllable positioning device is provided which includes a motor operated by a controller to automatically vary the tilt angle in response to sensed vibrations.
Vibration is also a problem when using a wet press of a papermaking machine. In such wet presses, as the felt and paper web to be drained are simultaneously conducted through a roll gap, water is pressed out of the paper web and transferred onto the felt web. The absorbed water is removed from the felt at another point along its closed loop path by, for example, a suction roll. The pairs of rolls forming the roll gap, along with their guides which engaged roll journals and the elastically resilient felt, form a vibrating system with a large number of resonance vibrations that can be excited during operation of the web press.
U.S. Pat. No. 5,785,636 to Bonander discloses a roll having an outer surface made of a fabricated fiber matrix for strengthening and reinforcing the roll to maximize roll stability.
U.S. Pat. No. 4,301,582 to Riihinen discloses a system that removes deflections from a roll using magnetic forces. The roll has a non-rotating axle with ends having a load imposed thereat and a cylindrical shell rotatably supported by bearings on the axle. A magnetic core is formed in the axle and a plurality of pole shoes are spaced from the shell by an air gap. A plurality of electromagnetic windings, each wound on the core at one of the pole shoes, produce a magnetic compensating force field between the shell and the core for responding to deflections in the roll.
U.S. Pat. No. 4,357,743 to Hefter, et al., discloses a controlled deflection roll having a roll shell which is radially movable in at least one plane in relation to a roll support. Position feelers or sensors are arranged at the ends of the roll shell for detecting one or more deflections in the roll shell as a function of deviations from a predetermined reference or set point. The position feelers control regulators operatively associated with pressure or support elements positioned between the roll support and the roll shell so that the roll shell is maintained in the reference or set position.
U.S. Pat. No. 4,062,097 to Riinhinen discloses a roll having magnetic deflection compensation that may be used in the calender or press section of a paper machine. The roll has an inner non-rotating axle and an outer shell surrounding and rotatable with respect to the axle, the axle and the shell having a common axis. The axle includes an inner magnetic structure while the shell includes an outer magnetic structure that rotates together with the shell. These inner and outer magnetic structures cooperate to provide attraction between the shell and axle on one side of the above axis and repulsion between the shell and axle on the opposite side of the axis, thereby achieving deflection control and/or compensation.
Other techniques used to reduce the detrimental effects of roll vibration include running process machinery at slower speeds in order to avoid resonance problems, and using back-up roll systems to reduce vibration.
Therefore, there is a need to have a vibration control system for a dynamic surface that damps or eliminates vibrations in the dynamic surface. There is also a need for a vibration control system that enables vibrations to be induced into a dynamic surface for any purpose necessary.
The present invention addresses the above-identified problems by providing a system and method for controlling vibration of a dynamic surface. In its broadest sense, the present invention may be used to eliminate undesirable vibrations from a dynamic surface or to actively induce vibrations into the dynamic surface. In preferred embodiments, the present invention may be used to control vibration of a dynamic surface on any object that rotates including, but not limited to, a roll that engages a web, a gear, wheels and/or tires. The present invention may also be used to reduce or control vibrations in aerodynamic surfaces or one or more surfaces of a loom. In highly preferred embodiments, the inventive system includes at least one piezoelectric actuator in communication with the dynamic surface of a roll and a mass overlying the piezoelectric actuator so that the piezoelectric actuator is between the mass and the dynamic surface for controlling vibration of the roll and/or actively inducing vibration into the roll.
As is well known to those skilled in the art, piezoelectric elements may be used to covert electrical energy into mechanical energy and vice versa. For nanopositioning, the precise motion that results when an electric field is applied to a piezoelectric material is of great value. Actuators using this effect have changed the world of precision positioning. As used herein, the term xe2x80x9cpiezoelectric actuatorxe2x80x9d means a piezoelectric device or element, or any electronic device that operates in a similar fashion to a piezoelectric element such as an electromagnet or a magnetostatic device.
As set forth herein, the term xe2x80x9cdynamic surfacexe2x80x9d means any surface that may change with respect to time, regardless of whether the change occurs over 5-10 seconds or over a time period as small as one microsecond. However, as microtechnology improves and microprocessors operate at faster speeds, it is contemplated that the present invention could be used for dynamic surfaces that change over a period of time as small as 1 nanosecond. The present invention may be used for a broad range of applications whereby the system components move at various speeds. For example, the vibration control system of the present invention can be used when making a paper web moving at approximately 5000 feet/minute, when making textile materials moving at approximately 100-300 feet/minute or when making paper maker""s clothing (PMC) moving at approximately 1-30 feet/minute.
In accordance with one aspect of the present invention, there is provided a system for controlling vibration of a dynamic surface, such as the exterior surface of a roll. The system preferably includes at least one sensor in communication with the dynamic surface for measuring vibration of the dynamic surface and generating a feedback signal upon measuring vibration. The feedback signal may be proportional to the velocity, displacement and/or acceleration of the measured vibration. The feedback signal may consist of one or more of these variables. As used herein, the term xe2x80x9cvibrationxe2x80x9d includes any dynamic surface response to any force to which the dynamic surface may be subjected including pressure forces, compressive forces, tensile forces, resonance, thermal action or other process forces. Moreover, the above-listed vibration forces may be applied in any direction with respect to the dynamic surface including directions that are substantially perpendicular to the dynamic surface and directions that are substantially parallel to the dynamic surface. The system also includes at least one piezoelectric actuator in communication with the dynamic surface and at least one mass overlying the at least one piezoelectric actuator so that the at least piezoelectric actuator lies between the mass and the dynamic surface.
The system also preferably includes a controller in communication with the at least one sensor for receiving the feedback signal and sending the output signal to the at least one piezoelectric actuator. If the feedback signal indicates that the dynamic surface is undergoing vibration, the piezoelectric actuator, upon receiving the output signal, applies a counter force between the dynamic surface and the mass upon receiving the output signal for reducing or controlling vibration of the dynamic surface. The at least one piezoelectric actuator may also be activated when no vibration is sensed in order to actively induce vibrations into the dynamic surface.
The application of piezoelectric elements to dynamic surfaces, such as the exterior surface of a roll, resolves vibration problems in a much more efficient manner than is available with the vibration control methods described above. Piezoelectric actuators can apply forces independently in various magnitudes, and in various combinations. This is not possible with most if not all of the existing roll control methodologies. Piezoelectric actuators are extremely precise, allowing repeatable nanometer and sub-nanometer movements. In addition, piezoelectric actuators can produce significant amounts of force over relatively small areas and are capable of moving heavy loads of up to several tons. Moreover, because piezoelectric elements derive their motion through solid state crystal effects and have no moving parts the response time of piezoelectric elements is in the kilohertz range so that they may be activated at very high frequencies. Finally, piezoelectric elements require very little power and require no maintenance.
The at least one piezoelectric actuator preferably includes a plurality of piezoelectric actuators that are provided in contact with the dynamic surface. The piezoelectric actuators are preferably piezoelectric foils having a length of approximately 1 to 5 centimeters, a width of approximately 1 to 5 centimeters and a height of less than 1 centimeter. As such, one piezoelectric actuator preferably covers an area of approximately 1-25 cm2. In other preferred embodiments, piezoelectric actuators of any size and/or dimension may be used. Thus, the present invention is not limited to using actuators of the size/type listed above.
The present invention preferably applies a plurality of piezoelectric actuators in contact with the dynamic surface of a roll so that relatively large controlling forces may be applied to the dynamic surface. Because each piezoelectric actuator can be controlled separately by the controller, it is possible to impart virtually any type of vibration or shape in the dynamic surface that is desired, thereby providing for unlimited performance possibilities not available in prior art technologies.
In one preferred embodiment, the dynamic surface is preferably provided on a roll shell secured over a roll support. The roll shell may be a non-coated or a coated roll. The roll shell is preferably flexible and substantially cylindrical, has an interior surface defining an inner diameter of the roll shell and an exterior surface defining an outer diameter of the roll shell. The exterior surface of the roll shell preferably includes the dynamic surface. The sensors and piezoelectric actuators are preferably connected to the interior surface of the roll shell; and one or more masses overlie the piezoelectric actuators so that the piezoelectric actuators lie between the masses and the interior surface of the roll shell. In certain embodiments, the ratio of masses to piezoelectric actuators could be 1:1, however, in other embodiments the number of piezoelectric actuators may greatly exceed the number of masses or the number of masses may greatly exceed the number of piezoelectric actuators. In other embodiments, the sensors and piezoelectric actuators may be connected to either the inner or exterior surface of the roll shell or any combination thereof, so long as the masses overlie the piezoelectric actuators so that the piezoelectric actuators lie between the masses and the dynamic surface. In other embodiments, the sensors are in communication with, but not in contact with, the roll shells.
The roll shell preferably has a longitudinal axis and preferably rotates about a central axis substantially parallel to the longitudinal axis. The roll shell is desirably mounted on a roll shell support that supports rotation of the roll shell about the central axis thereof. The roll shell support may include an axle mounted to an external support structure. The axle may rotate.
In certain embodiments, the counter vibrating force applied by the piezoelectric actuators generates either a compressive force or a tensile force between the mass and the dynamic surface of the roll shell. The compressive and tensile forces are applied through the piezoelectric actuators and directly to the dynamic surface and the corresponding mass surfaces. The compressive and tensile forces are generally opposed to one another. In other words, the compressive forces compress the mass and the dynamic surface toward one another while the tensile forces urge the mass and the dynamic surface away from one another. The piezoelectric actuators may be aligned to exert compressive and tensile forces in directions substantially parallel to or substantially perpendicular to the longitudinal axis of the shell. The piezoelectric actuators may also be aligned to apply compressive and tensile forces to the dynamic surface in a plurality of various directions that are neither perpendicular to nor parallel to the longitudinal axis of the shell.
The vibration control system of the present invention preferably includes a plurality of sensors in communication with the shell. The sensors are designed for detecting and/or measuring the magnitude of the vibration of the dynamic surface of the shell. The sensors are preferably spaced apart from one another and interspersed between the piezoelectric actuators. In certain preferred embodiments, the piezoelectric actuators are aligned in rows over the interior surface of the shell and the sensors are interspersed between the piezoelectric actuators. The rows of aligned piezoelectric actuators may extend in directions substantially parallel to or perpendicular to the longitudinal axis of the shell, or may extend in any number of directions between those that are substantially perpendicular and those that are substantially parallel to the longitudinal axis of the shell. The ratio of piezoelectric actuators to sensors is preferably about 100:1. The sensor may be one of a wide variety of sensors including but not limited to a piezoelectric element, a strain gauge, a laser used in conjunction with a reflective element, an optical device, a capacitive device and/or a magnetic device. In other preferred embodiments, the ratio of piezoelectric actuators to sensors will vary. The ratio may be 1:1, or the number of sensors may outnumber the number of piezoelectric actuators.
The vibration control system of the present invention also preferably includes a controller having a microprocessor and a memory device. The memory may have stored therein look-up tables, a control strategy algorithm and/or an adaptive feedback control strategy algorithm. The controller is preferably designed for receiving feedback signals from the sensors. The controller then processes the feedback signals to determine the presence or absence of a vibration. If an undesirable vibration state is detected at one or more regions of the dynamic surface, the controller transmits output signals to the piezoelectric actuators at those vibrating regions for removing the vibrations. The control system of the present invention may also be used to actively induce vibrations into the dynamic surface.
In certain preferred embodiments, the system for controlling vibration of a dynamic surface may be utilized for a web support structure located between two rolls so as to support the web as it passes by the web support structure. In these particular embodiments, the web support structure includes a supporting element having a web support layer. The web support layer has a top surface including the dynamic surface and a bottom surface remote therefrom. The dynamic surface is designed to engage the web passing thereover, such as a web of partially formed paper moving over the dynamic surface during a paper forming process. The control system of the present invention may also be used for processing textile materials and/or paper maker""s clothing felts or any other process involving web handling. In these particular embodiments, the sensors and the piezoelectric actuators are provided in contact with the second surface of the web support layer and one or more masses overlie the piezoelectric actuators so that the piezoelectric actuators lie between the second surface of the web and the masses. However, in other embodiments, the sensors and piezoelectric actuators may be in contact with either the first surface or the second surface or any combination thereof, and the masses overlie the piezoelectric actuators. The dynamic surface of the web support layer may be substantially flat or have an arcuate section. In certain embodiments, the one or more sensors preferably determine the position of the dynamic surface in relation to the supporting element for detecting the presence of a deflecting force upon the dynamic surface.
In these embodiments, at least one of the piezoelectric actuators is sandwiched between the at least one mass and the interior surface of the shell. In certain applications, there is a need to operate rolls at a speed that coincides with the resonance of the roll. When operated at or near resonance, a roll""s dynamic response may cause detrimental effects on the roll itself, the machinery containing the roll and the process that the roll is completing. Using piezoelectric devices mounted between the roll (or other machine members) and a mass, and having the piezoelectric actuator connected to and controlled by a properly designed control device, vibrations in the dynamic surface of the roll can be reduced and/or controlled, thereby eliminating or reducing detrimental effects. Similarly, vibrations can be induced into rolls or other machine members for any purposes necessary.